From 162c1c1f115d3604c3621c84aeb71753563e25a5 Mon Sep 17 00:00:00 2001
From: Guido Trotter <ultrotter@google.com>
Date: Fri, 8 Feb 2008 11:23:40 +0000
Subject: [PATCH] Shared Lock implementation and unit tests.
Adding a locking.py file for the ganeti locking library. Its first component is
the implementation of a non-recursive blocking shared lock complete with a
testing library.
Reviewed-by: imsnah, iustinp
---
lib/locking.py | 193 ++++++++++++++++++++++++++++++++
test/Makefile.am | 3 +-
test/ganeti.locking_unittest.py | 160 ++++++++++++++++++++++++++
3 files changed, 355 insertions(+), 1 deletion(-)
create mode 100644 lib/locking.py
create mode 100755 test/ganeti.locking_unittest.py
diff --git a/lib/locking.py b/lib/locking.py
new file mode 100644
index 000000000..4e9911026
--- /dev/null
+++ b/lib/locking.py
@@ -0,0 +1,193 @@
+#
+#
+
+# Copyright (C) 2006, 2007 Google Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+"""Module implementing the Ganeti locking code."""
+
+# pylint: disable-msg=W0613,W0201
+
+import threading
+
+
+class SharedLock:
+ """Implements a shared lock.
+
+ Multiple threads can acquire the lock in a shared way, calling
+ acquire_shared(). In order to acquire the lock in an exclusive way threads
+ can call acquire_exclusive().
+
+ The lock prevents starvation but does not guarantee that threads will acquire
+ the shared lock in the order they queued for it, just that they will
+ eventually do so.
+
+ """
+ def __init__(self):
+ """Construct a new Shared Lock"""
+ # we have two conditions, c_shr and c_exc, sharing the same lock.
+ self.__lock = threading.Lock()
+ self.__turn_shr = threading.Condition(self.__lock)
+ self.__turn_exc = threading.Condition(self.__lock)
+
+ # current lock holders
+ self.__shr = set()
+ self.__exc = None
+
+ # lock waiters
+ self.__nwait_exc = 0
+ self.__nwait_shr = 0
+
+ def __is_sharer(self):
+ """Is the current thread sharing the lock at this time?"""
+ return threading.currentThread() in self.__shr
+
+ def __is_exclusive(self):
+ """Is the current thread holding the lock exclusively at this time?"""
+ return threading.currentThread() == self.__exc
+
+ def __is_owned(self, shared=-1):
+ """Is the current thread somehow owning the lock at this time?
+
+ This is a private version of the function, which presumes you're holding
+ the internal lock.
+
+ """
+ if shared < 0:
+ return self.__is_sharer() or self.__is_exclusive()
+ elif shared:
+ return self.__is_sharer()
+ else:
+ return self.__is_exclusive()
+
+ def _is_owned(self, shared=-1):
+ """Is the current thread somehow owning the lock at this time?
+
+ Args:
+ shared:
+ < 0: check for any type of ownership (default)
+ 0: check for exclusive ownership
+ > 0: check for shared ownership
+
+ """
+ self.__lock.acquire()
+ try:
+ result = self.__is_owned(shared)
+ finally:
+ self.__lock.release()
+
+ return result
+
+ def acquire(self, blocking=1, shared=0):
+ """Acquire a shared lock.
+
+ Args:
+ shared: whether to acquire in shared mode. By default an exclusive lock
+ will be acquired.
+ blocking: whether to block while trying to acquire or to operate in try-lock mode.
+ this locking mode is not supported yet.
+
+ """
+ if not blocking:
+ # We don't have non-blocking mode for now
+ raise NotImplementedError
+
+ self.__lock.acquire()
+ try:
+ # We cannot acquire the lock if we already have it
+ assert not self.__is_owned(), "double acquire() on a non-recursive lock"
+
+ if shared:
+ self.__nwait_shr += 1
+ try:
+ # If there is an exclusive holder waiting we have to wait. We'll
+ # only do this once, though, when we start waiting for the lock. Then
+ # we'll just wait while there are no exclusive holders.
+ if self.__nwait_exc > 0:
+ # TODO: if !blocking...
+ self.__turn_shr.wait()
+
+ while self.__exc is not None:
+ # TODO: if !blocking...
+ self.__turn_shr.wait()
+
+ self.__shr.add(threading.currentThread())
+ finally:
+ self.__nwait_shr -= 1
+
+ else:
+ self.__nwait_exc += 1
+ try:
+ # This is to save ourselves from a nasty race condition that could
+ # theoretically make the sharers starve.
+ if self.__nwait_shr > 0 or self.__nwait_exc > 1:
+ # TODO: if !blocking...
+ self.__turn_exc.wait()
+
+ while len(self.__shr) > 0 or self.__exc is not None:
+ # TODO: if !blocking...
+ self.__turn_exc.wait()
+
+ self.__exc = threading.currentThread()
+ finally:
+ self.__nwait_exc -= 1
+
+ finally:
+ self.__lock.release()
+
+ return True
+
+ def release(self):
+ """Release a Shared Lock.
+
+ You must have acquired the lock, either in shared or in exclusive mode,
+ before calling this function.
+
+ """
+ self.__lock.acquire()
+ try:
+ # Autodetect release type
+ if self.__is_exclusive():
+ self.__exc = None
+
+ # An exclusive holder has just had the lock, time to put it in shared
+ # mode if there are shared holders waiting. Otherwise wake up the next
+ # exclusive holder.
+ if self.__nwait_shr > 0:
+ self.__turn_shr.notifyAll()
+ elif self.__nwait_exc > 0:
+ self.__turn_exc.notify()
+
+ elif self.__is_sharer():
+ self.__shr.remove(threading.currentThread())
+
+ # If there are shared holders waiting there *must* be an exclusive holder
+ # waiting as well; otherwise what were they waiting for?
+ assert (self.__nwait_shr == 0 or self.__nwait_exc > 0,
+ "Lock sharers waiting while no exclusive is queueing")
+
+ # If there are no more shared holders and some exclusive holders are
+ # waiting let's wake one up.
+ if len(self.__shr) == 0 and self.__nwait_exc > 0:
+ self.__turn_exc.notify()
+
+ else:
+ assert False, "Cannot release non-owned lock"
+
+ finally:
+ self.__lock.release()
+
diff --git a/test/Makefile.am b/test/Makefile.am
index d2af6b35a..3eed00002 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -2,7 +2,8 @@ TESTS = \
ganeti.config_unittest.py \
ganeti.hooks_unittest.py \
ganeti.utils_unittest.py \
- ganeti.bdev_unittest.py
+ ganeti.bdev_unittest.py \
+ ganeti.locking_unittest.py
TESTS_ENVIRONMENT = PYTHONPATH=.:$(top_builddir)
diff --git a/test/ganeti.locking_unittest.py b/test/ganeti.locking_unittest.py
new file mode 100755
index 000000000..bd2691b36
--- /dev/null
+++ b/test/ganeti.locking_unittest.py
@@ -0,0 +1,160 @@
+#!/usr/bin/python
+#
+
+# Copyright (C) 2006, 2007 Google Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 0.0510-1301, USA.
+
+
+"""Script for unittesting the locking module"""
+
+
+import os
+import unittest
+import time
+import Queue
+
+from ganeti import locking
+from threading import Thread
+
+
+class TestSharedLock(unittest.TestCase):
+ """Shared lock tests"""
+
+ def setUp(self):
+ self.sl = locking.SharedLock()
+ # helper threads use the 'done' queue to tell the master they finished.
+ self.done = Queue.Queue(0)
+
+ def testSequenceAndOwnership(self):
+ self.assert_(not self.sl._is_owned())
+ self.sl.acquire(shared=1)
+ self.assert_(self.sl._is_owned())
+ self.assert_(self.sl._is_owned(shared=1))
+ self.assert_(not self.sl._is_owned(shared=0))
+ self.sl.release()
+ self.assert_(not self.sl._is_owned())
+ self.sl.acquire()
+ self.assert_(self.sl._is_owned())
+ self.assert_(not self.sl._is_owned(shared=1))
+ self.assert_(self.sl._is_owned(shared=0))
+ self.sl.release()
+ self.assert_(not self.sl._is_owned())
+ self.sl.acquire(shared=1)
+ self.assert_(self.sl._is_owned())
+ self.assert_(self.sl._is_owned(shared=1))
+ self.assert_(not self.sl._is_owned(shared=0))
+ self.sl.release()
+ self.assert_(not self.sl._is_owned())
+
+ def testBooleanValue(self):
+ # semaphores are supposed to return a true value on a successful acquire
+ self.assert_(self.sl.acquire(shared=1))
+ self.sl.release()
+ self.assert_(self.sl.acquire())
+ self.sl.release()
+
+ def testDoubleLockingStoE(self):
+ self.sl.acquire(shared=1)
+ self.assertRaises(AssertionError, self.sl.acquire)
+
+ def testDoubleLockingEtoS(self):
+ self.sl.acquire()
+ self.assertRaises(AssertionError, self.sl.acquire, shared=1)
+
+ def testDoubleLockingStoS(self):
+ self.sl.acquire(shared=1)
+ self.assertRaises(AssertionError, self.sl.acquire, shared=1)
+
+ def testDoubleLockingEtoE(self):
+ self.sl.acquire()
+ self.assertRaises(AssertionError, self.sl.acquire)
+
+ # helper functions: called in a separate thread they acquire the lock, send
+ # their identifier on the done queue, then release it.
+ def _doItSharer(self):
+ self.sl.acquire(shared=1)
+ self.done.put('SHR')
+ self.sl.release()
+
+ def _doItExclusive(self):
+ self.sl.acquire()
+ self.done.put('EXC')
+ self.sl.release()
+
+ def testSharersCanCoexist(self):
+ self.sl.acquire(shared=1)
+ Thread(target=self._doItSharer).start()
+ self.assert_(self.done.get(True, 1))
+ self.sl.release()
+
+ def testExclusiveBlocksExclusive(self):
+ self.sl.acquire()
+ Thread(target=self._doItExclusive).start()
+ # give it a bit of time to check that it's not actually doing anything
+ self.assertRaises(Queue.Empty, self.done.get, True, 0.2)
+ self.sl.release()
+ self.assert_(self.done.get(True, 1))
+
+ def testExclusiveBlocksSharer(self):
+ self.sl.acquire()
+ Thread(target=self._doItSharer).start()
+ time.sleep(0.05)
+ self.assertRaises(Queue.Empty, self.done.get, True, 0.2)
+ self.sl.release()
+ self.assert_(self.done.get(True, 1))
+
+ def testSharerBlocksExclusive(self):
+ self.sl.acquire(shared=1)
+ Thread(target=self._doItExclusive).start()
+ time.sleep(0.05)
+ self.assertRaises(Queue.Empty, self.done.get, True, 0.2)
+ self.sl.release()
+ self.assert_(self.done.get(True, 1))
+
+ def testWaitingExclusiveBlocksSharer(self):
+ self.sl.acquire(shared=1)
+ # the lock is acquired in shared mode...
+ Thread(target=self._doItExclusive).start()
+ # ...but now an exclusive is waiting...
+ time.sleep(0.05)
+ Thread(target=self._doItSharer).start()
+ # ...so the sharer should be blocked as well
+ self.assertRaises(Queue.Empty, self.done.get, True, 0.2)
+ self.sl.release()
+ # The exclusive passed before
+ self.assertEqual(self.done.get(True, 1), 'EXC')
+ self.assertEqual(self.done.get(True, 1), 'SHR')
+
+ def testWaitingSharerBlocksExclusive(self):
+ self.sl.acquire()
+ # the lock is acquired in exclusive mode...
+ Thread(target=self._doItSharer).start()
+ # ...but now a sharer is waiting...
+ time.sleep(0.05)
+ Thread(target=self._doItExclusive).start()
+ # ...the exclusive is waiting too...
+ self.assertRaises(Queue.Empty, self.done.get, True, 0.2)
+ self.sl.release()
+ # The sharer passed before
+ self.assertEqual(self.done.get(True, 1), 'SHR')
+ self.assertEqual(self.done.get(True, 1), 'EXC')
+
+
+if __name__ == '__main__':
+ unittest.main()
+ #suite = unittest.TestLoader().loadTestsFromTestCase(TestSharedLock)
+ #unittest.TextTestRunner(verbosity=2).run(suite)
--
GitLab